How do you use a full backup taken in the Local-standby (not the primary) to create the Remote-standby?
Any pointers will be appreciated...essentially creating a standby from a standby.

It may be of interest to note that running the "BACKUP CURRENT CONTROLFILE FOR STANDBY" in the Local-standby will error out with:
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of backup command on dupdb_ch1 channel at 11/30/2012 19:49:44
ORA-01671: control file is a backup, cannot make a standby control file

For folks who may stumble on this thread.
2 hosts - 1 - primary, 2 - local stby
3rd host was being added in the mix.
So, we want to build standby number 3 - DR stby

Aim was to create the DR stby from a backup taken from local stby, W/O affecting primary.

Create backup pieces from local stby (to be made available in DR stby) using "backup device type disk format '/u01/backups' database plus archivelog;"
As mseberg pointed out, take a "backup current controlfile for standby" from primary & make it available in DR stby
startup nomount the DR stby
restore controlfile in DR from step2
catalog the backup taken in step 1
Run the duplicate command from DR as usual, connecting to the primary as target and the DR as auxiliary